The present invention relates to network systems. More specifically, the invention relates to a node apparatus having an interface with a virtual-connection-oriented network and a method for managing a virtual connection to transmit packets from the node apparatus.
To transfer packets through a virtual connection in a virtual-connection-oriented network, such as an ATM (Asynchronous Transfer Mode) network, a virtual connection is set up one of two ways:
1) all virtual connections between nodes in the network are set up in advance of using the virtual connections to transfer packets (e.g., PVC (Permanent Virtual Connection) or VP (Virtual Path) in the ATM network); or PA1 2) an adequate virtual connection is set up when it is required in order to transfer packets, and it is released when the transfer of packets terminates (e.g., SVC (Switched Virtual Connection) in the ATM network).
The first method makes it possible to use a virtual connection without waiting for setup when a node is starting to transmit a packet. However, a prior setup of all virtual connections by a human network manager has great difficulties. In addition, in the PVC method, it is difficult to determine how many virtual connections to preset. In the VP method, the usage of virtual connections may be inefficient because many virtual connections of the fixed number (e.g., 2.sup.16) are necessarily set up between all neighboring nodes.
The second method sets up a virtual connection from a first node to a second node by, for example, ATM signaling when the first node is transmitting a packet to the second node, and releases the virtual connection by ATM signaling when the first node finishes transmitting packets to the second node. Because the setup of a virtual connection starts after the virtual connection becomes necessary, a delay due to the setup exists until the node becomes able to transmit the packet. Moreover, the frequency of setup/release of virtual connections is high because the virtual connection is released each time it becomes unnecessary. This require the highest performance nodes and switches in the network for in setup/release signaling.